Patent GB-1133031-A (GB)
Title: Load sensitive vehicle brake system
IPC: B60T8/18
Filed: 1965-11-16
Abstract: 1,133,031. Fluid-pressure brakes; dashpots; springs. MIDLAND-ROSS CORP. 16 Nov., 1965 [11 Jan., 1965], No. 48646/65. Headings F2F and F2S. In a load-sensitive fluid-pressure, e.g. compressed-air, brake system for a vehicle supported on an axle via an air or mechanical spring suspension and equipped with brake means for the associated wheels, a load-responsive proportioning valve 42 comprises a housing 50 providing cylinders 72, 74 containing pistons 68, 70, a lever arm 94 extending between the pistons the undersides of which it engages via balls 92 and sockets 90, 96, a movable fulcrum 67 for the arm formed on a slide block 66 which is movable by an arm 150 carried by a shaft 146, the shaft 146 being rotatable in accordance with movements of the spring suspension, and a valve assembly controlled by the piston 70 and comprising a tubular member 106 which is formed to provide a flange 108 fitted with an inlet valve 110 co-operating with a seat opening 104 and whose lower end is engageable with a diaphragm 85 arranged in the cylinder 74 so as to lie against the top of the piston 70, the diaphragm and member 106 thus providing an exhaust valve. A further diaphragm 76 lies against the top of the piston 68, the two diaphragms rendering unnecessary the usual piston seals whereby friction of the moving parts is reduced. Oscillations of the suspension are damped by hydraulic damper pistons 174 working in cylinders 170, the cylinders and the interior of the housing being filled with oil and a valve assembly for permitting flow through passages 190 in each of the pistons only in the direction from the housing interior into the respective cylinder consisting of a resilient disc 186 covering openings 180 in the piston and retained thereon by a stem 184. Reverse flow can take place slowly between the peripheries of the unsealed pistons and the cylinder walls. Connecting-rods 158 connect the pistons to the slide block 138. The rate of movement of the slide block is arranged to be independent of that of the suspension by interposing between the shaft 146 and a lever 194 connected to the suspension an assembly comprising a pre-stressed compression spring 214, Fig. 7, trapped between arms of a fork 208 secured to the shaft 146, the lever 194 being secured to a split housing 200, 202 which has a sector-shaped cavity enclosing the fork and spring, abutments 220 in the interior of the housing being adapted to act on opposite ends of the spring to increase its compression and thereby transmit a force proportional to axle movement to the slide block 138. In an alternative arrangement suitable for an air suspension, Fig. 9, the air spring pressure acts on a piston assembly 256 which is sealed by a diaphragm 248 and itself contains a piston 280 integrally formed on an output rod 240 which is adjustably linked to an operating lever (224, Fig. 8, not shown) carried by the shaft 146. A passage 290 in the rod 240 connects atmosphere to one side of piston 280 which is also acted on by compression spring 268, while air spring pressure is communicated via passage 288 to the other side of piston 280. As air spring pressure rises the assembly 256 moves to the right to compress a spring 292 and also the spring 268, the latter determining the force transmitted to the output shaft 240, and hence to the slide block 138. The type "A" system shown in Fig. 1 incorporates proportioning valves 42 in both front and rear axle brake circuits so that pedal pressure for a given deceleration is constant in all conditions of loading, each circuit comprising a relay valve 24, controlled by a pressure derived from that supplied by a driver's valve 38, modified by the relevant proportioning valve 42, to control the supply of air via the relay valve from a reservoir 32 to the appropriate front or rear axle brakes. In a modified type "B" system (Fig. 2, not shown) a proportioning valve (42) is provided only in the rear axle circuit, this being suitable where it is permissible or desirable for pedal pressure for a given rate of deceleration to vary in accordance with the load on the front axle.